A sun-tanned appearance is a symbol of a healthy, dynamic, and active life. Yet, the damaging effects of sunlight and other sources of ultraviolet radiation on the skin are well documented. These effects are cumulative and potentially serious, and include sunburn, skin cancer, and premature aging of the skin. These effects associated with exposure to ultraviolet radiation are more fully discussed in DeSimone, "Sunscreen and Suntan Products", Handbook of Nonprescription Drugs, 7th Ed., Chapter 26, pp. 499-511 (American Pharmaceutical Association, Washington, D.C.; 1982); Grove and Forbes, "A Method for Evaluating the Photoprotection Action of Sunscreen Agents Against UV-A Radiation", International Journal of Cosmetic Science, 4, pp. 15-24 (1982); and U.S. Pat. No. 4,387,089, DePolo, issued Jun. 7, 1983; the disclosures of all of which are incorporated herein by reference in their entirety.
Sunscreens are the most common agents used for sun protection. However, sunscreens also have the disadvantage of preventing or greatly diminishing the cosmetically desirable tanning response. Thus, if an individual uses a sunscreen for protection from ultraviolet radiation, he or she does so at the expense of foregoing a tanned appearance. Furthermore, even if an individual is willing to accept the risks associated with exposure to ultraviolet radiation to obtain a tan, there are situations in which it may not be practical or even possible to do so because of time constraints, weather conditions, etc. Therefore, it would be highly desirable to develop products for providing a tanned appearance to the skin, whenever desired without the need for exposure to ultraviolet radiation.
It is generally known that dihydroxyacetone, when applied topically to human skin, will produce a tanned appearance, i.e. an artificial tan. U.S. Pat. No. 4,708,865, to Turner, issued Nov. 24, 1987 describes the use of hydro-alcoholic solutions of dihydroxyacetone for tanning the skin; U.S. Pat. Nos. 4,466,805, to Welters, issued Aug. 21, 1984 describes hair and skin coloring formulations containing dihydroxyacetone; and 2,949,403, to Andreadis et al., issued Aug. 16, 1960 describes artificial tanning formulations containing dihydroxyacetone in an oleaginous base.
Dihydroxyacetone is relatively sensitive to heat, light, and moisture. It is known that products containing dihydroxyacetone generally have a short shelf life, tending to darken and develop disagreeable off-odors over time, with a concomitant loss of product performance.
Dihydroxyacetone can react with other ingredients in a formulation, especially with nitrogen-containing compounds, such as amines, amino acids, and the like. In fact, without being limited by theory, dihydroxyacetone is believed to provide an artificial tan to human skin by its reaction with the nitrogen containing proteins of the skin. See L. Goldman et al., "Investigative Studies with the Skin Coloring Agents Dihydroxyacetone and Glyoxal", The Journal of Investigative Dermatology, vol. 35, pp. 161-164 (1960); E. Wittgenstein et al., "Reaction of Dihydroxyacetone (DHA) with Human Skin Callus and Amino Compounds", The Journal of Investigative Dermatology, vol. 36, pp. 283-286 (1961); and A. Meybeck, "A Spectroscopic Study of the Reaction Products of Dihydroxyacetone With Amino Acids", J. Soc. Cosmet. Chem., 25-35 (1977); all of which are incorporated by reference herein in their entirety. These stability and incompatibility problems have limited the scope of artificial tanning products in the past.
Many artificial tanning products also have the disadvantage of not providing the desired control over color development of the tan. Artificial tans are often either too light or too dark, and tend to be too orange, uneven, or unnatural in appearance. Artificial tans often take too long to develop--sometimes as long as several hours or overnight. Also, it is known that some individuals are "non-reactors" or "inadequate reactors" in that these individuals do not develop an artificial tan with dihydoxyacetone or develop an artificial tan to only a slight extent. Therefore, a need exists to develop artificial tanning compositions that are chemically and physically stable, are aestheically pleasing to use, that provide improved color development characteristics, and that provide an artificial tan for non-reacting and inadequately reacting individuals.
It is well known that various chemical compounds can be used to modify or enhance the tanning reaction obtained with dihydroxyacetone on human skin. Examples of such compounds include amino acids. See, e.g. Kawashima et al., "Nonenzymatic Browning Reactions of Dihydroxyacetone With Amino Acids or Their Esters", Agric. Biol. Chem. 44(7), 1595-1599 (1980), and M. F. Bobin et al., "Effects of Color Adjuvants On the Tanning Effect of Dihydroxyacetone", J. Soc. Cosmet. Chem., 35 265-272 (August 1984), both of which are incorporated by reference herein in their entirety.
It is generally known that the reaction of dihydroxyacetone with amino acids is difficult to control and has been an obstacle to successfully using amino acids in combination with dihydroxyacetone in an artificial tanning composition. For example, when dihydroxyacetone is formulated with an amino acid, the composition tends to undergo an unacceptable discoloration reaction during storage. A possible solution to this problem is to formulate the dihydroxyacetone separately from the amino acids and to deliver the separate formulations either sequentially from separate containers or simultaneously from a dual-chambered dispensing device. However, these alternatives are inconvenient, cumbersome, and expensive to implement and use. See, e.g. European Patent No. 527,864, assigned to Unilever, published Jun. 23, 1993.
The present invention utilizes certain amino acids or their pharmaceutically acceptable salts to modify the artificial tanning reaction of dihydroxyacetone with skin to provide improved color development characteristics. The present invention solves the longstanding incompatibility problem between the amino acids (or their pharmaceutically acceptable salts) and dihydroxyacetone through two different types of embodiments. In one set of embodiments, the compositions are formulated at a pH value below about pH 4. Without being limited by theory, it is believed that at these low pH values, the amino acid exists primairly in a form whereby the amino groups are protonated and essentially rendered inactive with the dihydroxyacetone to provide a composition that is suitably stable for storage in a packaged product. Upon application to the skin, it has been found that these stable compositions provide the desired artificial tanning reaction from the dihydroxyacetone, the amino acid, and the skin. It is believed that when these compositions are contacted with the skin, which typically has a pH value greater than about 4, that the protonated amino sites on the amino acid are neutralized and rendered reactive with the dihydroxyacetone to yield the desirable artificial tanning reaction with the skin. See E. T. Bernstein et al., "The Acidity On The Surface Of The Skin", N.Y. State J. Med., vol. 92, pp.436-442 (1942); H. C. Korting et al., "Influence of Repeated Washings With Soap And Synthetic Detergents On pH and Resident Flora Of The Skin Of Forehead And Forearm", Act. Derm. Venereol (Stockh), vol. 67, pp. 41-47 (1987); and A. Zlotogorski, "Distribution Of Skin Surface pH On The Forehead And Cheek Of Adults", Arch. Dermatol Res., vol. 279, pp. 398-401 (1987), all of which are incorporated by reference herein in their entirety, which discuss the skin pH phenomenon.
In other embodiments of the present invention, stable artificial tanning compositions containing dihydroxyacetone and an amino acid are achieved over a wide range of pH values (i.e. not limited to pH values of about 4 or below) by also utilizing a stabilizing salt selected from the group consisting of metabisulfite salts, sulfite salts, and hydrogen sulfite salts. These compositions also provide improved development characteristics.
It is therefore an object of the present invention to provide compositions for imparting an artificial tan to human skin.
It is another object of the present invention to provide artificial tanning compositions formulated below a pH value of about 4 having a high degree of chemical and physical stability comprising both dihydroxyacetone and certain amino acids for modifying the artificial tan development.
It is another object of the present invention to provide artificial tanning compositions having a high degree of chemical and physical stability comprising dihydroxyacetone, certain amino acids, and stabilizing salt selected from the group consisting of metabisulfite salts, sulfite salts, hydrogen sulfite salts, and mixtures thereof.
It is another object of the present invention to provide artificial tanning compositions having improved color development characteristics.
It is another object of the present invention to provide artificial tanning compositions which are aesthetically pleasing to use.
It is another object of the present invention to provide artificial tanning compositions useful for both providing an artificial tan to human skin and for protecting human skin from the harmful effects of ultraviolet radiation.
It is another object of the present invention to provide a method for artificially tanning human skin.
It is another object of the present invention to provide a method for artificially tanning human skin and for providing protection from the harmful effects of ultraviolet radiation.
These and other objects of this invention will become apparent in light of the following disclosure.